Use of endoparasites, Ligula intestinalis plerercoid in ...

Chromium showed site specific bioaccumulationby parasites showing higher concentration of metalcontent between parasites and host in site 2. This mayindicate environmental influence on the heavy metal,rather than the measured contents in fish that mayinterfere with the physiological functions of theparasites in the host. In site 2, we observed golddeposits along the river bed that may interfere with themetal accumulation in the fish. This variability, reflectthe mobility of the fish host and can obscure thedifferences that might be detected between sites.When the metal accumulation in fish parasitesand fish was compared in the enriched lake waterfrom site 1, the results are as shown in Tab. 3. Inenriched lake water, there was higher bioaccumulationof metals by a ranging from 10 times to 35.Bioaccumulation is a well documented field ofresearch (Rainbow, 2007; Zimmermann et al., 2004;Sizmur and Hodson, 2009). Normally,bioaccumulation of metals is through highly specificphysiological uptake mechanisms (Chapman, 1997;Rainbow, 2007) and reflects its exposure to pollutantsover time. Metals accumulate more rapidly than canbe eliminated due to low molecular weights, metalbinding proteins, such as metallothioneins (MT’s) andpresent in aquatic organisms. In addition, MT’scontrol the bioavailability and the kinetics ofbioaccumulation as well as the toxic effects that occurvia the induction of their biosynthesis (Baudrimont etal., 2003). For most fish, these intracellular proteinsbind specifically and have a high affinity for metals,such as Cd, Cu and Zn.In the aquatic environment, factors that canaffect bioaccumulation of metals include:environmental conditions, presence of specificbioavailable metal species (Rainbow and Dallinger,1993; Van Ginneken et al., 1999), trophic status ofbioaccumulation, physiological condition of theorganism, interactions between metals and the uptakeand release rates (kinetics) of metals by an organism(Buchwalter and Luoma, 2005). In fish-parasiteassociation, the normal physiological functioning offish is interrupted though it is not clear, which amongthese factors will exert great control over metals in thefish system.Metal concentration in L. intestinalis (mg kg -1 dw)the parasite tissues, albeit the increased Pb and Crcontent in parasite relative to the fish tissues was morepredictable than the changes in Cd (Fig. 3). Thissuggest an uptake of metal by parasites from the fishtissues as the metal content in R. argentea increasecomparable to the studies involving heavy metaluptake kinetics in parasites in fish tissues. On theother hand, increased Cu burden in the fish tissues wasassociated with linear reduction of the Cu in thetissues of the parasites. The present decline in Cu inparasite host as it increases in fish host was interpretedas elemental competition for essential element.Parasites and fish host have been shown to competefor several elements such as Ca, Cu, Fe, Zn and Sr inperch (Sures, 2002). Though there is paucity of dataon studies dealing with simultaneous analysis ofdifferent elements in fish, and even less studiesdealing with metal kinetic and metal metabolism infish-parasite association, it is probable thatcompetition for elements between host and parasitesfor essential elements could lead to increasedabsorption of other essential metals including Cu.Concentrations of Cu may be regulated by the fish aswell as by the parasite, albeit the physiologicallyrequired levels are actually higher in the parasite.These higher Cu concentrations should therefore notbe construed as bioaccumulation of environmentalpollutants.50.040.030.020.010.00.05.04.03.02.01.0Pb y = 3.6564x + 1.273R 2 = 0.57220.0 2.0 4.0 6.0 8.0 10.0Cr14.0y = 4.2418x + 0.9463R 2 = 0.60012.402.001.601.200.800.4012.010.08.0Cd y = 7.1748x + 0.3049R 2 = 0.4240.05 0.10 0.15 0.20 0.25Cuy = -0.9226x + 15.835R 2 = 0.4985Tab. 3 Heavy metal concentration in fish, parasite andthe overall bioaccumulation factor0.00.0 0.2 0.4 0.6 0.8 1.0 1.26.03.0 4.0 5.0 6.0 7.0 8.0Heavy metal concentrationBioconcentrationHeavymetals Fish Parasite factorPb36.22 ± 4.2 421.65 ± 10.2 11.6Cd0.78 ± 0.12 27.6 ± 1.92 35.4Cr3.95 ± 0.42 42.65 ± 1.44 10.8Cu11.01 ± 1.12 102.4 ± 5.55 10.2Increased content of Pb, Cd and Cr in R. argentearesulted to corresponding increase of these metals inFig. 3. Regression models showing the relationshipsbetween metal concentration (mg kg -1 dw) in L.intestinalis against metal concentration in Ligulaintestinalis4. ConclusionHeavy metal concentration in R. argentea (mg kg -1 dw)The present study shows that the L. intestinalis inR. argentea accumulates heavy metals in variablequantities in fish host. Some heavy metals such as Pb,Cd and Cr were bio accumulated by upto factor 11, 18and 14 respectively and Cu by factor 2.5 in the fish4